Export to Excel from gridview in c#

protected void ImageButton1_Click(object sender, ImageClickEventArgs e)

{

Response.ClearContent();

Response.Buffer = true;

if (chkall.Checked == true)

{

Response.AddHeader("content-disposition", string.Format("attachment; filename={0}", "calls report of alluser"+txtfromdate.Text+" "+"to"+" "+txttodate.Text+".xls"));

}

else

{

Response.AddHeader("content-disposition", string.Format("attachment; filename={0}", "calls report of user" + " " + ddlagent.SelectedItem.Text + ".xls"));

}

Response.ContentType = "application/ms-excel";

StringWriter sw = new StringWriter();

HtmlTextWriter htw = new HtmlTextWriter(sw);

reportgrid.AllowPaging = false;

getgrid();

//Change the Header Row back to white color

reportgrid.HeaderRow.Style.Add("background-color", "#afabc4");

//Applying stlye to gridview header cells

for (int i = 0; i < reportgrid.HeaderRow.Cells.Count; i++)

{

reportgrid.HeaderRow.Cells[i].Style.Add("background-color", "#afabc4");

}

int j = 1;

//This loop is used to apply stlye to cells based on particular row

foreach (GridViewRow gvrow in reportgrid.Rows)

{

gvrow.BackColor = Color.White;

if (j <= reportgrid.Rows.Count)

{

//if (j % 2 != 0)

//{

for (int k = 0; k < gvrow.Cells.Count; k++)

{

gvrow.Cells[k].Style.Add("background-color", "#FFFFFF");

}

//}

}

j++;

}

reportgrid.RenderControl(htw);

Response.Write(sw.ToString());

Response.End();

}